In the current broadcasting system, media transport schemes of an MPEG-2 TS (Moving Picture Experts Group-2 Transport Stream) scheme and an RTP (Real-time Transport Stream) scheme are widely used. In these schemes, when attempting to cooperatively operate broadcasting and communication, various limitations arise. Therefore, MMT (MPEG Media Transport) is proposed as a new media transport scheme assuming the use of a variety of networks by utilizing MPEG.
In the case of authenticating a message in a transmission system adopting the MMT, a message authentication code is generated to prevent manipulating MMTP (MPEG Media Transport Protocol) packets. The authentication code generating apparatus adds a generated message authentication code to the end. of a payload of an MMTP packet and outputs the packet. The authentication code generating apparatus outputs a message authentication scheme identifier that is a value for distinguishing a message authentication scheme by including it in a message authentication scheme descriptor in a CA (Conditional Access) message or a PA (Package Access) message.
As a mechanism for detecting manipulated packets, a checksum which is used in a UDP (User Datagram Protocol) is known. In a UDP, a checksum is calculated using UDP headers, pseudo headers, and data of UDP payload parts. If the checksum is replaced with an MMT scheme, the authentication code generating apparatus is to generate a message authentication code using data from headers to payload parts of MMTP packets.
In some cases, in a transmission system adopting an MMT, a processor constituting the system may rewrite content of an MMTP packet. For example, when outputting MMTP packets, a multiplexing apparatus in a transmission system rewrites a value of at least either a time stamp or a packet counter included in an MMTP packet in accordance with a state of the MMTP packet at the time of outputting. Thus, in a case of rewriting content of an MMTP packet by a processor, a need of recalculating a message authentication code by the processor may arise. In a case of recalculating a message authentication code for each processor, the processor needs to be implemented with the authentication code generating unit for generating a message authentication code.
The authentication code generating unit may operate, for example, as described below. The authentication code generating unit detects an MMTP packet which is a CA message or PA message, and extracts a message authentication scheme descriptor from the detected CA message or PA message. The authentication code generating unit ascertains a message authentication scheme from the extracted message authentication scheme descriptor. The authentication code generating unit recalculates a message authentication code in accordance with the ascertained message authentication scheme for the MMTP packet for which its content is rewritten. Or, the authentication code generating unit recalculates a message authentication code for all the MMTP packets, and rewrites the message authentication scheme descriptor in the CA message or PA message.